Extending open core protocol to support system-level cache coherence

Abstract

Open Core Protocol (OCP) is a standard on-chip core interface specification. The current release is flexible and configurable to support the communication needs of a wide range of Intellectual Property cores, and is now in widespread use. However, it does not support system-level coherence. This paper summarizes an effort within the OCP-IP cache coherence working group on incorporating cache coherence extensions into OCP, which is expected to have strong impact on the MPSoC industry. In this paper, we propose a backward-compatible coherent Open Core Protocol interface and discuss the design challenges and implications introduced. This interface is flexible and can support a range of coherence protocols and schemes: we show how it can specify a snoopy bus-based scheme as well as a directory-based scheme. The correctness of the specification and models was verified using NuSMV, via exploring the entire state space for the two basic coherence schemes.